4 ms·

> A swarm whose members are in known spatial positions relative to each other, having state-of-the-art microminiaturized clocks to keep synchrony, can utilize i

by davedx 2y ago

> A swarm whose members are in known spatial positions relative to each other, having state-of-the-art microminiaturized clocks to keep synchrony, can utilize its entire population to communicate with Earth, periodically building up a single short but extremely bright contemporaneous laser pulse from all of them. Operational coherence means each probe sends the same data but adjusts its emission time according to its relative position, such that all pulses arrive simultaneously at the receiving arrays on Earth. This effectively multiplies the power from any one probe by the number N of probes in the swarm, providing orders of magnitude greater data return. This sounds unfeasible. They have no way to keep station from what I understand, the interstellar medium is relatively empty but there will still be some drift over the light years. Having all of these independent craft synchronize and overlay their signals precisely enough for it to be receivable on Earth seems implausible. Can you say hella attenuation? I'd like to see some numbers...

uoaei 2y ago
Can you say relativistic corrections hell? "Over lightyears" means it takes literally years for these things to coordinate moves with each other, to say nothing of post-launch coordination messages from Earth.
- mlyle 2y ago
  > "Over lightyears" means it takes literally years for these things to coordinate moves with each other The swarm ends up around 100,000km wide. Initial distances are longer, but never on the order of light years.
  - maxrecursion 2y ago
    Yeah, I think he missed the part where it discussed the swarm would have to be mostly autonomous since communicating back to earth for any sort of management commands is completely out of the question. It's amazing they can still do it with voyager which is roughly 24 hours for one way traffic, 48 for round trip.
  - uoaei 2y ago
    I'm not sure "swarm over interstellar distances" makes any sense here, then. How many stars are within 100,000 km of each other and what percentage of stars does that represent?
    - mlyle 2y ago
      The idea is, you launch a large number of probes, accelerated one by one, working so that they'll arrive at the same time to the same star (Proxima Centauri). If you lose a bunch, no problem. They'll be spread out over a big distance, but team up to do imaging and to return data from that star.
      - SideburnsOfDoom 2y ago
        > They'll be spread out over a big distance Compared to the distance that you'd go to get a coffee, yes. Compared to the distance to Proxima Centauri, oh hell no. Compared to that distance, they travel as a pack. There's about a "402 million to 1" ratio between the two distances, 100 000km size of the swarm vs the 40,208,000,000,000 km distance to Proxima Centauri. https://imagine.gsfc.nasa.gov/features/cosmic/nearest_star_info.html https://imagine.gsfc.nasa.gov/features/cosmic/nearest_star_i... A swarm 100 000km wide could in its entirety pass between the Earth and the Moon with room to spare. https://www.nasa.gov/wp-content/uploads/2009/07/180561main_ETM.Distance.Moon_.pdf https://www.nasa.gov/wp-content/uploads/2009/07/180561main_E...
        mlyle 2y ago
        Yes, of course. We all know these numbers. I teach a space engineering class where students chirp out in recitation "400km to LEO, 40,000 km to GEO, 400,000 km to the moon". The degree of "well acktually" trying to be pedantic here is unnecessary. If a swarm of bees goes a couple of miles away, they don't spread out over a couple of mile distance. They are a relatively tight pack that then goes to the new place and then converges to be quite small. That's the same as what this mission is. 100,000 km is quite small as far as interstellar distances are concerned, but quite big as far as an aperture for distributed imaging or beamforming (and for avoiding hazards that are hard to see beforehand). The latter, of course, is what actually matters.
mlyle 2y ago
They don't need to keep exact position; they just need to know their relative distance offsets from Earth to synchronize pulses. They can do some work to keep station; the idea is that by adjusting attitude, they can adjust the magnitude and direction of their drag vector. https://arxiv.org/abs/2309.07061 https://arxiv.org/abs/2309.07061 It's absolutely infeasible with current technology, but it doesn't look like it's total unobtanium.
- deleted 2y ago
  [deleted]
nynx 2y ago
station keeping is definitely possible. each craft could use its comms laser for impulse
qnleigh 2y ago
I agree. Sounds like the plan is to have the signals from each probe add up coherently, which means the laser pulses need to be coherent with each other. The wavelength of optical light is 100s of nanometers, so that is the level of precision required spatially, relative to the much much larger probe spacing that they quote. This (plus the required temporal coherence) is probably not possible without the probes actively locking their lasers to each other, but now each probe needs the optics to send and detect the optical signal from at least its nearest neighbors. I can't say if this is impossible given the weight restrictions, but it sounds rough.

by davedx 2y ago

uoaei 2y ago

Can you say relativistic corrections hell? "Over lightyears" means it takes literally years for these things to coordinate moves with each other, to say nothing of post-launch coordination messages from Earth.

mlyle 2y ago
> "Over lightyears" means it takes literally years for these things to coordinate moves with each other The swarm ends up around 100,000km wide. Initial distances are longer, but never on the order of light years.
- maxrecursion 2y ago
  Yeah, I think he missed the part where it discussed the swarm would have to be mostly autonomous since communicating back to earth for any sort of management commands is completely out of the question. It's amazing they can still do it with voyager which is roughly 24 hours for one way traffic, 48 for round trip.
- uoaei 2y ago
  I'm not sure "swarm over interstellar distances" makes any sense here, then. How many stars are within 100,000 km of each other and what percentage of stars does that represent?
  - mlyle 2y ago
    The idea is, you launch a large number of probes, accelerated one by one, working so that they'll arrive at the same time to the same star (Proxima Centauri). If you lose a bunch, no problem. They'll be spread out over a big distance, but team up to do imaging and to return data from that star.
    - SideburnsOfDoom 2y ago
      > They'll be spread out over a big distance Compared to the distance that you'd go to get a coffee, yes. Compared to the distance to Proxima Centauri, oh hell no. Compared to that distance, they travel as a pack. There's about a "402 million to 1" ratio between the two distances, 100 000km size of the swarm vs the 40,208,000,000,000 km distance to Proxima Centauri. https://imagine.gsfc.nasa.gov/features/cosmic/nearest_star_info.html https://imagine.gsfc.nasa.gov/features/cosmic/nearest_star_i... A swarm 100 000km wide could in its entirety pass between the Earth and the Moon with room to spare. https://www.nasa.gov/wp-content/uploads/2009/07/180561main_ETM.Distance.Moon_.pdf https://www.nasa.gov/wp-content/uploads/2009/07/180561main_E...
      - mlyle 2y ago
        Yes, of course. We all know these numbers. I teach a space engineering class where students chirp out in recitation "400km to LEO, 40,000 km to GEO, 400,000 km to the moon". The degree of "well acktually" trying to be pedantic here is unnecessary. If a swarm of bees goes a couple of miles away, they don't spread out over a couple of mile distance. They are a relatively tight pack that then goes to the new place and then converges to be quite small. That's the same as what this mission is. 100,000 km is quite small as far as interstellar distances are concerned, but quite big as far as an aperture for distributed imaging or beamforming (and for avoiding hazards that are hard to see beforehand). The latter, of course, is what actually matters.

mlyle 2y ago

They don't need to keep exact position; they just need to know their relative distance offsets from Earth to synchronize pulses. They can do some work to keep station; the idea is that by adjusting attitude, they can adjust the magnitude and direction of their drag vector. https://arxiv.org/abs/2309.07061 https://arxiv.org/abs/2309.07061 It's absolutely infeasible with current technology, but it doesn't look like it's total unobtanium.

deleted 2y ago
[deleted]

nynx 2y ago

station keeping is definitely possible. each craft could use its comms laser for impulse

qnleigh 2y ago

I agree. Sounds like the plan is to have the signals from each probe add up coherently, which means the laser pulses need to be coherent with each other. The wavelength of optical light is 100s of nanometers, so that is the level of precision required spatially, relative to the much much larger probe spacing that they quote. This (plus the required temporal coherence) is probably not possible without the probes actively locking their lasers to each other, but now each probe needs the optics to send and detect the optical signal from at least its nearest neighbors. I can't say if this is impossible given the weight restrictions, but it sounds rough.